Physiological Age Factors
Understand the science behind the physiological factors that shape your Biological Age.
Physiological Factors and Biological Age
Your Biological Age is built on three groups of factors: physiological, lifestyle, and blood biomarkers. This article covers the physiological factors (sleep, activity, and fitness metrics) drawn from your wearable and health data.
These factors are averaged across the past four weeks in Bevel. Each one is compared against optimal health standards for your age and sex, and the research behind them draws on long-term studies measuring mortality risk. Bevel then applies hazard ratios from that research to estimate how each factor contributes to your Biological Age, while accounting for overlap between related metrics so that no single effect is double-counted.
Sleep
Time Asleep
How many hours you sleep each night; the foundation of recovery, hormone regulation, immune function, and metabolic health.
The research:
- Sleeping 6 hours is associated with a 13% higher all-cause mortality risk vs. 7 hours
- Sleeping 5 hours: 29% higher risk
- Sleeping 10+ hours: 36% higher risk
- Both too little and too much carry risk (Wang et al., 2021)
In Bevel: 7.5–9 hours → subtracts years. Consistently outside that range in either direction → adds years.
Sleep Consistency
How stable your sleep and wake times are day to day, including weekends. A key marker of circadian health.
The research:
- Low sleep regularity is associated with a 53% higher all-cause mortality risk vs. average
- High sleep regularity is associated with ~10% lower risk (Windred et al., 2024)
- Sleep regularity was found to be a stronger predictor of mortality than sleep duration (Huang et al., 2023)
In Bevel: Consistency above 70% → subtracts years. An irregular schedule → adds years, independent of total sleep time.
Activity
Daily Steps
Total daily movement, including workouts, walking, errands, and everything in between.
The research:
- 8,000 steps/day → 51% lower mortality risk vs. 4,000 steps
- 12,000 steps/day → 65% lower risk (Saint-Maurice et al., 2020)
- Benefits level off at 6,000–8,000 steps for adults 60+, and 8,000–10,000 for adults under 60 (Paluch et al., 2022)
In Bevel: Under 60 → 8,000+ steps subtracts years. 60+ → threshold is 6,000 steps. Below those levels → adds years.
Zones 2–3 (Moderate Aerobic)
Time spent at moderate intensity is the foundation of cardiovascular fitness and metabolic health. Guidelines recommend 150+ minutes per week.
The research:
- 1–2x the weekly recommended minimum → 31% lower mortality risk vs. inactive adults
- 2–3x the minimum → 37% lower risk (Arem et al., 2015)
In Bevel: 150+ minutes/week in Zones 2–3 → subtracts years. Less than 150 minutes/week → adds years.
Zones 4–5 (Vigorous Activity)
Higher-intensity effort that challenges your cardiovascular system and improves fitness capacity, even in small doses.
The research:
- Vigorous activity associated with meaningful mortality reductions, with no evidence of harm even at very high volumes (Arem et al., 2015)
- Just 4.5 minutes/day of vigorous activity is associated with a 31–32% lower cancer risk compared with adults who do no structured exercise (Stamatakis et al., 2023)
In Bevel: Just 10+ minutes/week in Zones 4–5 → subtracts years. A little vigorous effort goes a long way.
Strength Training
How regularly you perform resistance exercise; one of the most important habits for preserving muscle, bone, and metabolic health over time.
The research:
- Any resistance training is associated with a 21% lower all-cause mortality risk (Saeidifard et al., 2019)
- Greatest benefit seen at ~60 minutes/week: 15% lower all-cause, 19% lower cardiovascular, 14% lower cancer mortality (Shailendra et al., 2022)
In Bevel: 10+ minutes/week → subtracts years. Even small, regular amounts matter. Too little → adds years.
Fitness
VO₂ Max
Your body's maximum capacity to take in and use oxygen during exercise and one of the strongest predictors of longevity in all of health science. The American Heart Association recommends it as a clinical vital sign.
The research:
- Elite fitness vs. low fitness: 80% lower all-cause mortality risk, a 5x difference (Mandsager et al., 2018)
In Bevel: Compared against optimal standards for your age and sex. Excellent VO₂ Max → subtracts years. Lower → adds years. This is one of the highest-impact factors in the model.
Resting Heart Rate
How many times your heart beats per minute at complete rest. A lower RHR reflects a more efficient cardiovascular system.
The research:
- Every 10 bpm increase in RHR is associated with a 9% higher all-cause mortality risk and 8% highercardiovascular mortality risk (Zhang et al., 2016)
In Bevel: Lower RHR → subtracts years. Higher RHR → adds years. Benchmarks are adjusted for your age and sex.
Lean Body Mass
The total weight of your body minus fat, including muscle, bone, organs, and water. A key marker of physical resilience, metabolic health, and functional capacity, especially as you age.
The research:
- Low lean body mass is associated with a 44–81% higher mortality risk (Li et al., 2021)
- Each 20-percentile increase in muscle index is associated with a 14% lower all-cause mortality risk (Cheng et al., 2025)
In Bevel: Compared against optimal standards for your age and sex. Lower lean body mass → adds years at any age. The benefits of higher lean body mass become more meaningful from your mid-30s onward, as natural muscle decline begins.
How These Factors Work Together
These nine metrics don't operate in isolation — many are biologically connected:
- VO₂ Max and Resting Heart Rate both reflect cardiovascular fitness
- Strength Training and Lean Body Mass are closely linked as cause and effect
- Zones 2–3 and VO₂ Max both respond to aerobic training volume
Because of this, Bevel accounts for overlap between correlated factors rather than treating each as fully independent. The individual year-impacts won't always sum to a clean total — but the combined estimate is more accurate because of it.
For a deeper dive into any factor, including how to interpret your score and tips for improvement, see the individual articles below:
